Instead of removing it’s best to set the WP_DEBUG to false.
1. The first two errors you should be able to fix by opening file wpadverts/includes/functions.php and on line about 1713 to 1730 replace the function
function adverts_save_multi( $post_id, $key, $value ) {
if( !is_array( $value ) ) {
$value = array( $value );
}
$post_meta = get_post_meta( $post_id, $key, false);
if( empty( $post_meta ) ) {
$post_meta = array();
} else if( ! is_array( $post_meta ) ) {
$post_meta = array( $post_meta );
}
$to_insert = array_diff($value, $post_meta);
$to_delete = array_diff($post_meta, $value);
foreach( $to_delete as $meta_value ) {
delete_post_meta( $post_id, $key, $meta_value );
}
foreach( $to_insert as $meta_value ) {
add_post_meta( $post_id, $key, $meta_value );
}
}
with
function adverts_save_multi( $post_id, $key, $value ) {
if( !is_array( $value ) ) {
$value = array( $value );
}
$post_meta = get_post_meta( $post_id, $key, false);
$to_insert = array_diff($value, $post_meta);
$to_delete = array_diff($post_meta, $value);
foreach( $to_delete as $meta_value ) {
delete_post_meta( $post_id, $key, $meta_value );
}
foreach( $to_insert as $meta_value ) {
add_post_meta( $post_id, $key, $meta_value );
}
}
A similar update will be in next WPAdverts release.
2. The all other errors seem to be occurring because you have media files deleted from wp-content/uploads folder but the entries for this attachments are still in the wp_posts table (with post_type = attachment).
You would need to remove the attachments which does not have files. You can do that by going to wp-admin / Media Library panel and deleting permanently all files which have an empty preview or for which the preview link returns a 404 error.
